The present invention relates to an apparatus for printing, and more particularly to an apparatus having a displaceable print cylinder for printing on board or cut sections of board.
Apparatus for printing on board or cut sections of board, such as corrugated board, commonly include a number of print stations through which the board is directed to successively receive print images from one or more of the print stations.
In such apparatus, each print station commonly includes a print cylinder fitted with one or more printing plates for receiving ink from, for example, an anilox roll, and for transferring appropriate print images to the board or board sections. The printing plate or plates on each print cylinder need to be replaceable to enable different printing requirements to be satisfied. The present invention is concerned with an arrangement for enabling the printing plates to be changed on one print cylinder without requiring the entire printing apparatus to be stopped.
In addition, existing apparatus typically exhaust air from their vacuum transfer table fans directly into overhead centralized take-away systems or to a bag filter. Bag filters eventually clog, and the resulting back pressure decreases the vacuum level of the transport table. This decrease in vacuum level affects the accuracy of registration from one print unit to another. The present invention incorporates a self cleaning filter unit directly on the print unit""s vacuum fan""s exhaust to satisfy clean air requirements for operating personnel.
According to the present invention, at least one of the print stations comprises a print cylinder mounted in a laterally displaceable carriage which can be moved laterally (in a direction parallel to the longitudinal axis of the print cylinder) away from the board travel line, leaving in place substantially all the remaining parts of the print station, to allow changing of the printing plate or plates on the print cylinder while the printing apparatus can continue to operate with one or more of the other print stations.
Each print station is preferably a top printer: that is to say, it applies print to the upper surface of the board or board sections. In a preferred arrangement for flexographic printing, the print cylinder receives ink on its printing plate or plates from an anilox roll which remains in position (except for being moved slightly away from the print cylinder) when the print cylinder carriage is displaced laterally to allow the printing plate or plates to be changed.
Each print station preferably includes conveyors, for example rollers, for conveying the board through the station, and those conveyors remain in place when the print cylinder carriage is displaced laterally. Thus the conveyors remain available to convey board through the print station so as to allow the printing apparatus to continue operating while any given print station is being altered in preparation for applying the print needed for a subsequent order.
This invention contrasts with, and is an improvement over, prior proposals, for example one providing for the entire printer or the top portion thereof to be lifted vertically to allow the operator (who must then work on an overhead gantry) to change the printing plates. Another prior proposal involved displacing laterally the entire print station; this involves a number of problems, not least of which is the fact that the printing apparatus cannot then readily be kept in operation while one of the print stations is out of position. The provision, in accordance with the present invention, for displacing essentially only the print cylinder and leaving the remainder of the printing station in position is a significant improvement over such prior proposals.